Transistors in which the gate electrode forms a Schottky junction with the semiconductor substrate have been known in the art (see, e.g., JP-A-62-130567, JP-A-61-203672, JP-A-61-183961, and JP-A-5-211175.)
Suitable examples of gate electrode materials include tantalum nitride (TaN). A gate electrode formed of TaN can provide an appropriate Schottky barrier height Φb and an appropriate ideality factor (n-value) and have high moisture resistance.
However, if the transistor is stored under high temperature conditions with the TaN gate electrode exposed to ambient atmosphere, the gate electrode and the immediately underlying semiconductor substrate suffer nitrogen dissociation and oxidation, resulting in reduced reliability of the device under elevated temperature conditions.